1. Field of the Invention
The present invention relates generally to the fields of medical devices and medical diagnostics and treatment. More specifically, the present invention relates to an intravaginal radiofrequency imaging device for intravaginal monitoring to assess the function, morphology, and exercise-induced metabolic and biochemical changes in the pelvic floor muscles surrounding the vaginal vault.
2. Description of the Related Art
Magnetic resonance imaging can be used for imaging of physiologic function, in addition to anatomical imaging. One such area is in the imaging of muscular function, both cardiac and skeletal muscle. A method for quantifying the contractile function of the heart is known as radiofrequency (RF) tagging. In this method, image data readout is preceded by a composite radiofrequency excitation that produces a series of dark parallel lines in the image. These lines result from the selective saturation of tissue within the field of view (FOV). In cardiac imaging, this excitation would be delivered on the R-wave trigger (i.e. at end diastole). Since material points in the tissue have been saturated, the lines are seen during image playback to move with the tissue as the heart contracts. Two such excitations can be used on the R-wave trigger to produce a grid of lines. An important feature of this method is that such images can be analyzed using automated techniques to track the tag line motion, and thus produce maps of strain and shear, as well as strain and shear rates.
It is also possible to produce strain and shear maps illustrating the function of skeletal muscle when a triggering signal representing a reproducible stimulus can be produced. Contractile force or pressure is such a reproducible stimulus.
The pelvic floor muscles provide support for the bladder, bladder neck and urethra. Urinary leakage occurs due to hypermobility of the urethra subsequent to a laxity of these muscles which results in inadequate urethral compression during increases in intra-abdominal pressure such as with coughing, rising from a seated position, or exercising.
Exercise to recondition the muscles of the pelvic floor is not a new concept. Specificity of training is paramount to achieve optimal functioning of the muscle for its intended use (Astrand and Rodahl, 1986; Hortobaghi, et al., 1991). Muscles of the levator ani, collectively called the pelvic floor musculature (PFM), are a heterogeneous mixture of 70% Type I (slow twitch) and 30% Type II (fast twitch) fibers (Critchley, et al., 1980; Gilpin, et al., 1989; Parks, et al., 1977). Type II muscle fibers are further delineated into Type IIa and Type IIb fibers. Type IIa fibers have a preponderance of glycolytic enzymes in their mitochondria, are larger in diameter and fatigue very quickly. In contrast, Type IIb fibers have fewer glycolytic enzymes in their mitochondria, are smaller in diameter, and are more resistant to fatigue.
Kegel (1948) introduced pelvic floor musculature exercises four decades ago with reported 69-93% success rates in treating females with stress urinary incontinence (SUI) (Jones and Kegel, 1952; Kegel, 1951; Kegel, 1956; Kegel and Powell, 1950). Studies that have examined muscle response to training have targeted Type II muscle fibers in strength-training regimens to recondition the pelvic floor musculature (Bo, et al., 1990; Burns, et al., 1993; Dougherty et al., 1993). However, these investigators merely hypothesized the mechanism for improvement as being exercise-induced hypertrophy because studies to describe the pelvic floor musculature in regard to muscle fiber type and mechanism of action have been limited to in vivo biopsy at the time of surgery or cadaver dissection (Gilpin et al., 1989).
Although there have been many advancements in the treatment of urinary incontinence using pelvic floor muscle exercises within a behavioral framework, investigators have been unable to describe the precise mechanisms of improvement. There are many potential and competing theories for the mechanisms of action responsible for recovery of continence. Some have hypothesized that increasing muscle strength allows the patient better sphincter control, while others have suggested that with exercise, the muscle size increases to provide additional occlusive bulk around the urethral sphincter.
There is little agreement on the correct technique for performing pelvic floor muscle exercise (Wells, 1990), and few studies to determine contraction intensity level of exercise to ensure success in pelvic floor musculature exercise therapy (Dougherty et al., 1993). Furthermore, no in vivo studies have shown the dynamic biochemical and metabolic changes that occur during or as a result of pelvic floor musculature exercise.
Most exercise protocols to improve function of the pelvic floor musculature have targeted strength enhancement and have been successful in decreasing leakage episodes. Descriptions of specific muscular responses resulting in functional changes of the pelvic floor musculature are inconsistent between studies. Factors attributed to functional changes include increased vaginal pressures, lengthening of the functional area of the urethra, and initial neural adaptation. One study used graded pelvic muscle exercises to strengthen the pelvic floor musculature and enhance endurance of muscle contractions in 65 women aged 35-75 years (Dougherty et al., 1993). This 16-week exercise protocol required exercises three times per week with measurements taken every 4 weeks. Gradation of the exercises involved maximal contraction effort that increased in number of contractions over the protocol period. Endurance exercises were maximum effort with emphasis on sustaining the contraction for 10 seconds. The investigators hypothesized that sustained pressure would benefit the Type I muscle fibers, while the repeated maximum contraction effort would benefit the Type II muscle fibers. Decreases in grams of urine loss were statistically significant (t=xe2x88x924.7, p less than 0.0001). Episodes of leakage in 24 hours decreased from 2.6 to 1.0. There was no statistically significant correlation between urine loss and maximum pressure or between urine loss and sustained pressure. The investigators suggested that this finding might indicate that the mechanisms of pelvic floor musculature exercise affecting SUI are not explained by pressure changes alone. In fact, findings in a recent study (N=32) indicated that submaximal exercise not only increased endurance and resulted in decreases in quantity of urine leakage, but also was significantly more effective (t=1.75; p=0.045) for increases in strength of contraction effort than using a near-maximal exercise protocol (Johnson, 2001).
Technology is needed to enable investigators to describe the mechanisms responsible for improvement in continence. The ability to analyze the regional mechanical and metabolic changes that occur in the pelvic floor musculature as a result of exercise might facilitate determining which exercise protocols are more effective and at what intensity the greatest improvement occurs. Strain and shear maps can reveal the presence of asymmetric function, or a subtle muscle injury such as internal perineal tear from birth injury. Investigation of the phosphorus metabolites and the pH would provide a chemical xe2x80x9csnap-shotxe2x80x9d of the cellular metabolism which can reveal abnormalities such as reduced perfusion. However, current technology requires tissue biopsy to conduct this type of analysis. Nuclear MRI and spectroscopy using state-of-the-art techniques to describe changes in the pelvic floor musculature structurally during exercise and conduct biochemical and metabolic analyses as subjects exercise and improve over time, might give researchers insight into the mechanisms responsible for change and improvement without the need for invasive biopsy.
MRI has been used to visualize pelvic floor musculature contractions in normal females (N=6). Findings showed that pelvic floor musculature contractions using MRI could be identified and that anatomical displacement of the bladder could be demonstrated. This study used coronal and sagittal planes for imaging (Christensen et al., 1995). However, no study has reported use of an insertable vaginal device with incorporation of force transduction and phosphorus spectroscopy to allow investigators the ability to conduct force of contraction measurements and biochemical analyses without the need for tissue biopsy.
The prior art is deficient in the lack of a non-invasive device/means of intravaginal monitoring. Specifically, the prior art is deficient in the lack of an intravaginal imaging device for monitoring and conducting biochemical analysis, wherein the imaging device combines a NMR resonator and force transduction mechanism in a single device. The present invention fulfills this long-standing need and desire in the art.
The present invention provides a vaginal imaging probe (VIP), an intravaginal probe for quantifying morphological and biochemical changes in the pelvic floor muscles as well as monitoring muscular function. This vaginal imaging probe acts as a dual frequency (proton, 31phosphorus) transmit/receive antenna for magnetic resonance (MR) imaging and spectroscopy of the musculature which contributes to urinary continence. Additionally, the vaginal imaging probe incorporates a force transducer to measure the force of muscular contractions, and to permit triggering of image acquisitions according to the developed force levels.
In one embodiment of the present invention, there is provided a vaginal imaging device, comprising a single or dual tuned resonator and a force transduction mechanism to permit triggering of a scanner to produce vaginal nuclear magnetic resonance imaging and spectroscopy data. In one aspect, the resonator comprises a transmit/receive element which is a single turn solenoid oriented to permit non-gradient localized spectroscopy. Moreover, a vial containing a 300 mM inorganic phosphate reference solution is located at the center of the loop of the single turn solenoid to allow chemical shift referencing for the signals obtained. In another aspect, the transmit/receive element of the resonator is an array of individual antenna elements located around the long axis of the device for the purpose of providing a different spatial sensitivity profile than that provided by a single turn solenoid. The means to trigger the resonator can be provided by a piezoelectric force transducer, a resistive force transducer or a pneumatic pressure transducer. Such a vaginal imaging device is useful for radiofrequency tagged magnetic resonance imaging, phase velocity mapping, diffusion weighted imaging as well as non-gradient localized phosphorus spectroscopy.
In another embodiment of the present invention, there is provided a vaginal imaging device, comprising a single or dual tuned imaging and spectroscopy resonator and a force transducer encased in a magnetic resonance imaging compatible housing; a compliant and hollow disposable housing that allows pneumatic transduction of contraction effort; and a means to transmit the air pressure in the disposable housing to the force transducer. The resonator comprises a transmit/receive element which may be a single turn solenoid with a vial containing a 300 mM inorganic phosphate reference solution located at the center of the loop of the single turn solenoid to allow chemical shift referencing for the signals obtained. The force transducer can be a piezoelectric force transducer, resistive force transducer or pneumatic pressure transducer. Such a vaginal imaging device produces radiofrequency tagged magnetic resonance imaging and non-gradient localized phosphorus spectroscopy.
In other embodiments of the present invention, there are provided methods of imaging and assessing biochemical states in pelvic floor musculature in situations such as before and after exercise, before and after surgical repair and before and after pharmaceutical therapy in individual suffering from abnormalities in pelvic floor musculature.
Other and further aspects, features, and advantages of the present invention will be apparent from the following description of the presently preferred embodiments of the invention given for the purpose of disclosure.